New results on kaon decays from NA48

We report on recent results on rare and semileptonic kaon decays from NA48 and NA48/2. Using data from a minimum bias run in 1999 we present a new measurement of the CP violating decay KL → π+ π- with over 40000 selected events. We measured the ratio Γ (KL → π+ π-) / Γ (KL → π± e∓ ν) = (4.835 ± 0.038) × 10-3 leading to the precise determination of the CP violation parameter | η+ - | = (2.223 ± 0.013) × 10-3. From the same data we selected over 2 × 106 KL → π± μ∓ ν decays. Preliminary results from a dalitz plot fit yield the values for the form factors λ+ = 0.0260 ± 0.0007s t a t ± 0.0010s y s t and λ0 = 0.0120 ± 0.0008s t a t ± 0.0015s y s t. In one month of data taking in 2003 the NA48/2 experiment collected over 2 × 105 K± → π± π0 γ decays. A measurement of the relative contributions of Inner Bremsstrahlung, Direct Emission, and their interference is presented which results in f r a c (D E) = (3.35 ± 0.35s t a t ± 0.25s y s t) % and f r a c (I N T) = (- 2.67 ± 0.81s t a t ± 0.73s y s t) % showing for the first time a non-zero value of the interference term. © 2007 Elsevier B.V. All rights reserved.